During the assembly of electronics, various tools are used wherein the tool, such as a soldering iron, may provide a metal-to-metal contact with electrostatic discharge (ESD) sensitive components during the assembly process. If the soldering iron or other tool is defective or if the grounding of the tool is lost, sensitive components can be exposed to an excessive voltage that damages the components. For a soldering iron, there are two main sources of voltage on the tip of a typical soldering iron: poor grounding and induction. If the grounding of the soldering iron is missing or inadequate, then the voltage at its tip can be as high as ½ of the supply voltage to the iron. The grounding of a soldering iron can fail for many reasons including a defective electrical outlet, a missing grounding wire, grounding to a non-existing ground, etc. Even if grounding of the soldering iron is good, the tip of the soldering iron itself often does not have a consistent galvanic connection to the body of the soldering iron and, consequently, to ground. The lack of galvanic connection is due to either construction of the iron itself or to the fact that the tip works at a high temperature that promotes development of oxides that block galvanic contact. When the tip does not have the galvanic connection, the tip becomes capacitively coupled to the heating element of the soldering iron and can have excessive voltage on it that can be transferred to the sensitive components. It is desirable to avoid exposing the sensitive components to these voltages or currents from the tools used to assemble the electronics with the sensitive components.
A particular well known standard (Section 5.1.2.2 of MIL-STD-2000A) specifies that no more than 2 mV may exist on the tip of a soldering iron due to the concern for damaging the sensitive components. Various methods are used today to identify soldering iron with excessive voltage on its tip. For example, one known system checks the voltage on the tip of the soldering iron every time the tip comes into contact with a cleaning wet sponge that has a metal electrode underneath the sponge that is connected to a monitoring device. While this method does perform some monitoring of the voltage on the tip, the accuracy of this device is under question due to the uncertain resistance of the sponge that may vary radically depending on the amount of water in the sponge when the tip contacts the sponge. In addition, this system does not provide a direct method of testing the voltage since the circuit being assembled may have a different voltage on it for whatever reason as compared to the voltage applied to the sponge and the electrode that is measured using the device. In addition, there is no guarantee that the worker would use the sponge to clean the tip since other ways of cleaning the tip are available so that the voltage at the tip might not be regularly measured.
Due to the increasing sensitivity of electronics components, it is becoming more and more important to know at all times whether the soldering iron (or other tool) is exposing components to dangerous voltage levels. The above conventional system does not provide an adequate solution. Thus, it is desirable to provide a monitor device and method that overcomes the above limitations of the conventional system and it is to this end that the present invention is directed.